Polytetrafluoroethylene porous membranes are porous materials having countless fine holes thereinside, and are made of a polytetrafluoroethylene (hereinafter, referred to as a “PTFE)” excellent in heat resistance and chemical resistance. Polytetrafluoroethylene porous membranes are used in various applications, for example, used as filters in clean rooms, air conditioners, and turbines.
For example, Patent Literature 1 discloses a polytetrafluoroethylene porous material used for microfiltration filters and the like. The PTFE porous material is formed of a mixture of a PTFE having an average molecular weight of 2 million or more with a PTFE having an average molecular weight of 1 million or less.
Patent Literature 2 discloses a stretched porous polytetrafluoroethylene material containing a microstructure in which nodes are interconnected by fibrils for the purpose of giving heat stability to materials to be formed into a tape, a filament, a film, a stick, or a tube. The stretched porous polytetrafluoroethylene material includes a mixture of two different polymers. One of the polymers is a polytetrafluoroethylene homopolymer and the other is a modified polytetrafluoroethylene polymer.
Patent Literature 3 discloses a porous polytetrafluoroethylene prepared by mixing a high-molecular-weight emulsion polymer with a polytetrafluoroethylene radiation-chemically decomposed, and extruding the resulting mixture.
Patent Literature 4 discloses a porous stretched PTFE article that includes a stretched PTFE resin containing the first PTFE resin fine particles and the second PTFE resin fine particles. The first PTFE resin has a property to form more fibrils than the second PTFE resin, and the fibrils in the first PTFE resin are longer than those formed in the second PTFE resin. The second PTFE resin has a property to form nodes with a width greater than that of nodes formed in the first PTFE resin. The stretched PTFE article contains a plurality of nodes and fibrils and has a thickness of about 100 μm or larger.